1. Field of the Invention
The present invention generally relates to lens measuring instruments and, more particularly, is concerned with an eyewear lens mechanical or geometrical center locating apparatus.
2. Description of the Prior Art
Over the past century, various techniques have been employed in the art to locate the center of lenses in eyewear. The primary purpose in locating the center of the lenses is to make the distance between the centers of the lenses correspond to the wearer's interpupillary distance, that is, the distance between the pupils of the wearer's eyes.
One technique for determining the lens center is to use a measuring instrument having components in the form of circular protractor plates. Representative examples of such measuring instruments are the ones disclosed in U.S. Pat. No. 563,745 to Cole and U.S. Pat. No. 790,059 to Howland.
Another technique is to use a graphical device for determining the center of the lens. A representative example of such device is the one disclosed in U.S. Pat. No. 2,133,589 to Sterling.
Yet another technique for finding the lens center is to use a device having one or more movable members for positioning a lens being mounted on a support plate. Representative examples of such positioning devices are the ones disclosed in U.S. Pat. No. 3,981,081 to Welch, U.S. Pat. No. 4,077,722 to Bieskei and U.S. Pat. No. 4,693,573 to Zoueki.
For instance, the Welch patent discloses a lens measuring instrument utilizing a base plate, a L-shaped measuring member and a dial indicator attached to the measuring member that provides indicia regarding the distance between the measuring member and a reference member, both of which are supported on a transparent base. The Zoueki patent discloses an universal frame centering, holding and measuring device with a frame holder mounted on a base and two slidable rulers mounted perpendicular to the holder. There are vertical gradation indicia on the rulers for transcribing and checking of interpupillary distance.
While the aforementioned techniques may have functioned satisfactorily under the limited range of conditions for which they were designed, they share similar drawbacks in terms of their complexity to use and reliance on operator skill to achieve the desired level of accuracy. Consequently, a need still exists for an improved technique for locating the mechanical or geometrical center of an eyewear lens.